Hi stu,
Dump Valve and Blow off are the same thing more or less unless it is a re-circulator which is the one that
mitsubishi see fit to have installed.
If you want good advice then I suggest that you get an quality after market re-circulating dump valve which will do a better job as it is almost twice the size so there will be almost double the blow-off which will ultimately result in a more quicker and sharpen spool.
The other types are just for posing!
get your hands on a Forge or a HKS, trust me, you will feel the difference straight away on the pick-up and if you have a good Induction kit you will hear a pop on the gear change which sounds allot more rugged then a doosh!